Electrical transformer

ABSTRACT

An electrical transformer comprising a pressure tight casing completely enclosing a magnetic core having windings thereon with a dielectric fluid at least partially filling the casing. Pressure developed within the casing by heating of the windings is sensed by pressure sensitive means. An electrical signal circuit is activated by the pressure sensitive means and indicates the pressure level within the casing of the transformer to a remote observer. When the pressure within the casing exceeds a certain predetermined value, pressure relief means is activated and permits escape of the excess pressure. The electrical signal circuit indicates that the pressure relief means has been activated. The electrical signal circuit will remain activated until manually reset.

United States Patent 1191 Almand, III

1 ELECTRICAL TRANSFORMER [75] Inventor: Johnv Z. Almand, 111, Athens, Ga.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa. 22] Filed: Jan. 11, 1973 [21] Appl. No.: 322,829

52 US. Cl. 317/14'0, 317/14 J, 200/82 R,

. 137/538 [51] Int. Cl. H02h 7/04 [58] Field of Search 317/14 G, 14 H, 14 J; 200/82 R, 83 Z; 137/538 [56] References Cited UNITED STATES PATENTS 1,670,697 5/1928 Treanor 317/14 G 1,705,715 3/1929 Clark 317/14 G 1,751,222 3/1930 Styer 317/14 G 1,775,028 9/1930 Hilliard.. 317/14 G 1,899,746 2/1933 Brown 317/14 Gv 2,369,363 2/1945 Matthias 317/14 G 2,730,706 1/1956 Manke... 317/14 G 1 2,773,146 12/1956 Sauer 317/14 G 111] 3,816,801 ]June 11, 1974 2.896.662 7/1959 Thomas 137/538 Primary Examiner-William M. Shoop, Jr. Assistant Examiner-Patrick R. Salce Attorney, Agent, or Firm-F. E. Browder I ABSTRACT An electrical transformer comprising a pressure tight casing completely enclosing a magnetic core having windings thereon with a dielectric fluid at least partially filling the casing. Pressure developed within the 9 Claims, 9 Drawing Figures PATENTEUJUNHISYII I 3816L801 sumaura 1 ELECTRICAL TRANSFORMER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to electrical transformers, and in particular to electrical transformers having means for indicating pressure levels within the transformer.

2. Description of the Prior Art Since electrical transformers have enclosed within Y their casing a dielectric fluid, usually oil, excess pressure will develop within the casing as a result of the heating of the transformer windings. As the transformer windings reach an overload condition, they produce heat. The heat increases the oil temperature and causes the pressure within the casing of the transformer to increase. Some transformers are provided with pressure relief means which permits the escape of excess pressure from the casing. It would be beneficial to those utilizing the transformer to have available an indicating device which would denote the presence of an excess accumulation of pressure within the casing of the transformer. This information would be useful to the user of the transformer in determining, for example whether the transformer chosen for use is of a sufficient rating to perform the job required. Also, the safety hazard presented to workmen or bystanders if the transformer casing were to explode due to an excess of pressure therein could be eliminated by providing a prior warning of the excess pressure overload. An object of the invention, then, is to provide a transformer equipped to indicate that the pressure level within its casing is either approaching a critical condition, or has at a time in the immediate past experienced an overload condition.

SUMMARY OF THE INVENTION This invention discloses an electrical transformer having an electrical signal means which indicates externally to the transformer the pressure levels within the transformer casing. The electrical signal means indicates, in response to pressure sensitive means, that the transformer has at a time in the past had a pressure within its casing exceeding a predetermined value. When pressure relief means has been activated toallow the escape of this excess pressure, the electrical signal means continues to operate and indicate that the predetermined level of pressure within the casing has been reached. The electrical signal means will continue to operate until it is manually reset.

BRIEF DESCRIPTION OF THE DRAWINGS former showing another embodiment of the invention;

ing 12. The operation and interaction ducer element utilized in the embodiment shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar elements in all figures of the drawing.

Referring now to FIG. 1, a diagrammatic view of an electrical transformer embodying the teachings of this invention is illustrated. Although FIG. 1 shows an overhead distribution transformer, it is to be understood that the teachings of this invention could be applied to any electrical transformer apparatushaving a dielectric fluid disposed therein. A transformer 10 comprises an outer casing 12 enclosing a magnetic core 14 having a primary winding 16 and a secondary winding 18 disposed thereon. A dielectric fluid 20, preferably oil, surrounds the core 14, the primary winding 16 and the secondary winding 18. A pressure sensing means generally indicated at 22 senses the pressure within the casing 12. A pressure relief valve 24 operates to relieve the pressure within the casing 12 when the pressure exceeds a predetermined value. The casing 12 is generally fabricated of metal, or other suitable material, and has a top cover 26 and a bottom cover 28. The casing 12 supports and protects the components which are disposed within the casing 12. The transformer 10 is adapted for pole or cross arm mounting by a mounting bracket 30 disposed on the casing 12. Reference numeral 32 indicates the level of oil dielectric 20 disposed within the casing 12. A high voltage bushing 34 extends through the top cover 26 of the casing 12, and provides electrical insulation for a primary lead 36 which is connected to the primary winding 16. Electrical bushings 38 are disposed on the exterior of the casing 12, and provide electrical insulation for electrical leads 40 which are connected to the secondary winding 18. The casing 12 is maintained at a ground potential as indicated by reference numeral 42. Electrical signal means generally indicated at 44 is also disposed within the easof the pressure relief valve 24, the pressure sensing means 22, and the electrical signal means 44, will be discussed in greater detail herein.

Referring now to FIG. 2, a diagrammatic view of one embodiment of the invention is illustrated. FIG. 2 is a detail view of the pressure relief valve 24, the pressure sensitive means 22, and the electrical signal means 44. In this embodiment of the invention, the pressure sensitive means 22 is disposed so as to be external to the casing 12.

The pressure relief valve 24 is comprised of a cylinder 46 having .a piston 48 movably disposed within the cylinder 46, and a spring .50 mounted between the back wall of the cylinder 46 and the piston 48. An O-ring 52 circumferentially surrounds the piston 48 to provide a pressure tight seal with the inside wall of the cylinder 46. A conduit 54 communicates with the interior of the casing 12 and exposes the piston 48 to the pressure within the casing 12. The spring 50 exerts a force on the piston 48 which tends to push thepiston 48 toward the outer end of the conduit 54. Vent openings 60 in the cylinder 46 permit pressure within the cylinder 46 to vent to atmosphere once the piston 48 has moved far enough to expose one of the vent openings 60 to the pressure inside the conduit 54.

In general, the pressure sensitive means 22 is comprised of an abutment movable between a first and a second position, and means for biasing the abutment toward the first position. In the embodiment of the invention illustrated in FIG. 2, the pressure sensitive means 22 is comprised of a pilot tube 62 having a movable piston 64 disposed within the pilot tube 62. A spring 66 biases the movable piston 64 within the pilot tube 62. The pilot tube 62 communicates with the interior of the-casing 12. In the embodiment shown, the pilot tube 62 bifurcates from the conduit 54 of the pressure relief valve 24. It is to be understood, however, that any configuration whereby the pilot tube 62 directly communicates with the interior of the casing 12 is within the contemplation of this invention. An O-ring 68 surrounds the piston 64 and maintains a sealed relationship between the piston 64 and the inside of the pilot tube 62.

An L-shaped bracket 72 has a first portion 74 and a second portion 76. As viewed in FIG. 2, the first portion 74 is substantially horizontal while the second portion 76 is substantially vertical relative to the casing 12. The first portion 74 of the L-shaped bracket 72 is attached .to the'piston 64 in any convenient manner, as illustrated by a weld bead 78. The spring 66 is supported by a support member 80 which is mounted on The electrical signal means 44 is comprised of an electrical power source 86 connected in series to an electrical signal indicator 88 and a pressure responsive circuit element 90. The electrical power source 86 is any convenient source which can provide the energy necessary to energize the electrical signal means 44, such as a plurality of turns of the secondary winding 18,

, a separate winding on the transformer core 14, or a stepdown transformer; The electrical signal indicator 88 can be any'resistive circuit element, commonly an indicator light. ln this embodiment of the invention, the pressure responsive circuit element 90 is comprised of a movable stem ,92 supported by a support stem 94. The movable stem 92 is pivotally connected to a lug 96. The movable stem 92 is free to rotate around a pin 98 which attaches the movable stem 92 to the lug 96. The lug 9 6 is attached to the transformer casing 12. The support stem 94 is attached to the second portion 76 of the L-shaped bracket 72 by any convenient means, as indicated by a weld bead 100. The movable stem 92 and the support stem 94 are in contact at a cobtact point 102. The electrical power source 86, the electrical signal indicator 88, and the pressure responsive cirand the support stem 94) can be connected in any convenient circuit configuration. In the embodiment illustrated, the series circuit configuration is completed when the movable stem 92 and the support stem 94 are in contact, illustrated by the contact point 102. In this configuration when the contact point 102 is established between the movable stem 92 and the support stem 94, there is a voltage detectable across the electrical signal indicator 88.

However, alternative circuit configurations may be used, such as that indicated in FIG. 3. In this circuit configuration, an electrical contact 104 is disposed in the casing 12 and is connected in series to the electrical power source 86, the electrical signal indicator 88 and the pressure responsive circuit element 90. When the movable stem 92 is in contact with the support stem 94, illustrated by contact 102 (FIG. 2), the series circuit configuration of FIG. 3 is open and no voltage can be detected across the electrical signal indicator 88. However, when the movable stem 92 is in the position shown in the FIG. 3, electrical contact is established between the movable stem 92 and the electrical contact 104 and a voltage appears across the electrical signal indicator 88. This voltage indicates a predetermined pressure has been exceeded in the transformer casing 12.

When heating occurs in the primary winding 16 or the secondary winding 18, the oil dielectric 20 which surrounds these windings will experience a temperature rise. As a concommitan't to the rise in temperature of the oil dielectric 20, the pressure within the casing 12 will increase. Since .the casing 12 is pressure tight, it is possible that damage to the casing and the other components of the transformer will occur if the pressure within the casing 12 exceeds a predetermined value. In order to preclude any possible damage to the transformer, the pressure relief valve 24 becomes operable before the pressure in the casing 12 reaches a potentially dangerous level.

Since the casing 12 is pressure tight, and since the conduit 54 communicates with the interior of the easing 12, the pressure increase within the casing 12 will be sensed in the conduit 54. As the pressure increases within the casing 12, the pressure will exert a force on the piston 48. If the pressure in the casing 12 exceeds the predetermined value, the force exerted on the piston 48 by the pressure within the casing 12 will overcome the force exerted on the piston 48 by the spring 50. When the force exerted by the pressure on the piston 48 exceeds the force exerted by the spring 50 on the piston 48, the piston 48 will move in a direction indicated by arrow 106.

When the piston 48 moves a sufficient'distance 108 in the cylinder 46, the excess pressures within the casing 12 will be afforded an escape route through the openings of the pressure relief valve 24. In this manner, the excess pressures within the casing 12 can be released to atmosphere without damage to the transformer l0.

Since the pilot tube 62 also communicates with the interior of the casing 12, as the pressure within the cascuit element (comprised of the movable stem 92 ing 12 increases, this pressure increase is sensed in the pilot tube 62. When the pressure in the casing 12 increases, a force is exerted on the piston 64 disposed within the pilot tube 62. If the pressure within the casing 12 exceeds the certain predetermined value, the force exerted on the piston 64 by the pressure will overcome the force exerted on the piston 64 by the spring 66. When this occurs, the piston 64 will move from the normal first position 84 in a direction indicated by arrow 110. The amount of force required to be exerted on the piston 48 to overcome the force exerted by the spring 50 may differ from the amount of force necessary to overcome the force exerted by the spring 66 on the piston 64. Thus, the piston 48 may be biased by the spring 50 to move when a certain value of pressure, P is within the casing 12, whereas the'piston 64 may be biased by the spring 66 to move when a different value of pressure P is within the casing 12. As will be made apparent herein, for the invention to be most effectively utilized, the pressure P, which moves the piston '64 should be a lesser value than the pressure P which moves the piston 48, P, could, of course, be chosen to be equal to P As .the piston 64 which is disposed within the pilot tube 62 moves from the first position 84 in a direction indicated by arrow 110, the L-shaped bracket 72 will move in a corresponding direction. If a distance of travel 112 of the piston 64 within the pilot tube 62 is sufficient, the contact 102 between the support stem 94 and the movable stem 92 will be broken. When this occurs the movable stem 92 will'rotate around the pin 98 in the lug 96 and the movable stem 92 will fall in a direction indicated by arrow 114. The movable stem 92 will then occupy the final position indicated by the dotted line 116. This movement of the movable stem 92 will affect the electrical signal means 44 in a manner dependent upon the circuit configuration chosen. If the circuit configuration illustrated in the embodiment in FIG. 2, the movement of the support stem 94 and the movable stem 92' will result in the voltage previously detectable across the electrical signal indicator 88 dropping to a zero value. Thus, if the electrical signal indicator 88 werean indicator light, movement of the support stem 94 caused. by the increase in pressure within the casing 12 would cause the indicator light to be extinguished. However, if the circuit configuration illustrated in FIG. 3 were adopted, the movement of the movable stem 92 to position 116, FIG. 3, will establish contact at ll8 between the movable stem 92 and the electrical contact 104. This will result in a voltage appearing across the electrical signal indicator 88. Thus, if electrical signal indicator 88-were an indicator light,

the movement of the movable stem 92, caused by the increase in the pressure within casing 12, would cause the light to be energized.

For full effectiveness of the invention, the pressure P,, defined above, should be a value less than the pressure P also defined above, so that the force, F due to the pressure P within the casing 12. will act on the piston 64 at a point in time. earlier than the force F due to the pressure P will act on the piston 48 and trigger the pressure relief valve 24.

If the pressure within the casing 12. has been relieved by operation of the pressure relief valve 24, the force exerted by the pressurewithin the casing l2.against the piston 64 will not be sufficient to overcome theforces exerted against the piston 64 by the spring 66, and the piston 64 will be impelled. by thespring66 to return to the. first position 84. When this occurs, the support stem 94 will also return to its original position. However, since the movable stem 92Jhas occupied the final position indicated by the dotted line 116, the electrical signal indicator 88 will remain energized or de- 6 energized (depending on the circuit configuration chosen) after the operation of the pressure relief valve 24. The contact 102 between the support stem 94 and the movable stem 92 must then be re-established by a manual operation.

The pressure relief valve 24, however, has an automatic reset. Since the excess pressure within the casing 12 which exerted a sufficient force against the piston 48 to move the piston 48 in a direction 106 has been relieved, the force exerted by the spring 50 on the piston 48 will again become dominant.

By. utilization of the teaching of this invention, it is thus possible to indicate to an external observer that the pressure within the transformer casing 12 has exceeded the predetermined value, and also to provide a method of relieving the excess pressure.

Referring now to FIG. '4, a fragmented diagrammatic view of the interior of a transformer showing another embodiment of the invention is illustrated. In FIG. 4, a detail view of the pressure relief valve 24, the electrical signal means 44, and the pressure sensitive means 22 is illustrated. The pressure relief valve 24 is identical in construction to that described in conjunction with FIG. 2.

The electrical signal means 44 is comprised of the electrical power source 86 connected in series to the electrical signal indicator 88 and the pressure responsive circuit element 90. The electrical power source 86 is any convenient source which provides the energy necessary to energize the electrical signal means 44, such as a plurality of turns of the secondary winding 18, a separate winding on the transformer core 14, or a step down transformer. The electrical signal indicator 88 can be any resistive circuit element, such as, an indicator light. In this embodiment of the invention, the pressure responsive circuit element 90 is comprised of a vertical stem having a conducting pin 122 therein, the conducting pin 122 disposed within a nonconducting guide member 124 having a guide slot 125 therein'with an electrical contact 128 located at the bottom of the guide slot 125. The conducting pin 122 is attached at one end thereof to the vertical stem 120 by any convenient means. The vertical stem 120 and the guide member 124 are supported within the casing 12 by a plurality of support members 130, which are disposed in any convenient manner. Springs 132 are connected to the vertical stem 120 and conveniently disposed within the casing 12. The springs 132 facilitate the operation of the pressure responsive circuit element 90 in a manner to be described more fully herein. FIG. 5 illustrates a view along section VV of FIG. 4 of the pressure responsive circuit element 90. The electrical power source 86, the electrical signal indicator 88 and the pressure responsive circuit element 90 are connected in any convenient configuration. In the embodiment illustrated in FIGS. 4 and 5, the elec trical circuit means 44 is normally open and no voltage can be detected across the electrical signal indicator 88.

In general, the pressure sensitive means is comprised of an abutment movable between a first and second position and means for biasing the abutment toward the first position. In the embodiment of the invention illustrated in FIG. 4, the abutment movable between the first and second position and the means for biasing the abutment toward the first position are integral with the piston 48, the cylinder 46 and the spring 50 of the pressure relief valve 24. Thus, in this embodiment of the invention, the piston 48, the cylinder 46 and the spring 50 are elements common to boththe pressure relief valve 24 and the pressure sensitive means 22. In this embodiment of the invention, a horizontal stern 134 is mounted on the piston 48 by any convenient means, as indicated by a weld 136. The horizontal stem 134 of the pressure sensitive means 22 abuts the vertical stem 120 of the pressure responsive circuit element 90 as indicated at numeral 138. The abutment 138 between the horizontal stem 134 and the vertical stem 120 extends for a distance 140 on the vertical stem 120.

When heating occurs in the primary winding16 or the secondary winding 18, the corresponding temperature rise in the oil dielectric 20 causes an increase in the pressure within the casing 12. Since the casing 12 is pressure tight, and since the conduit 54 communicates with the interior of the casing 12, the pressure increase within the casing 12 will be sensed in the conduit 54. This increase in the pressure within the casing 12 will exert a force on the piston 48. If the pressure in the casing 12 exceeds thepredetermined value, the force exerted on the piston 48 by the pressure within the easing 12 will overcome the force exerted on the piston 48 by the spring 50. When the force exerted on the piston 48 by the pressure within the casing 12 exceeds the force exerted on the piston 48 by the spring 50, the piston 48 will move in a direction indicated by arrow 142. The excess pressures within the casing 12 will be afforded an escape route through the vent openings 60 of the pressure relief valve 24 and into the atmosphere. In

' a manner similar to that described previously, the excess pressure accumulating within the casing 12 can be relieved without damage to the transformer 10.

As the piston 48 is moved by the force exerted on it by the pressure within the casing 12, the horizontal stem 134 which is attached to the piston 48 will correspondingly move in the direction 142. As the horizontal stem 134 moves in the direction 142, the springs 132 will exert a force on the vertical stem 120, causing the vertical stern 120 to move in the direction illustrated by the arrow 144. If the horizontal stem 134 travels a sufficient horizontal distance 146, the conducting pin 122 will drop a vertical distance-148 in the guide slot 125 in the guide member 124. When the vertical stem 120 drops, the abutment 138 between the vertical stem 120 and the horizontal stem 134 will be broken, and the conducting pin .122 will be brought into direct contact with the electrical contact 128. When this occurs, the electrical signal means 44 will have a completed circuit configuration, and a voltage will appear across the electrical signal indicator 88. Thus,if the electrical signal indicator 88 were an indicator light, the indicator light would be energized due to the contact of conducting pin 122 with the electrical contact 128. The disposition of the elements in an operating position, as well as the completed circuit configuration, is illustrated in FIG. 6.

If the pressure within the casing 12 has been relieved by the operation of the pressure relief valve 24, the force exerted against the piston 48 by the pressure within the casing 12 will not be sufficient to overcome the force exerted on the piston 48 by the spring 50. The piston 48 will reoccupy its original position.

As the piston 48 returns to its original position, the horizontal stem 134 will also return to its original position. However, since the vertical stem 120 and the conducting pin 122 have dropped into the conducting seat also be manually re-established. The pressure relief.

valve will reset in a manner described previously in conjunction with FIG. 2.

By utilization of the teachings of this invention, it is thus possible to indicate to an external observer that the pressure within the transformer casing 12 has exceeded the predetermined value, and also to provide means to relieve the excess pressure.

Referring now to FIG. 7, a diagrammatic view of the interior of the electrical transformer utilizing another embodiment of the invention is illustrated. In FIG. 7, a detailed view of the pressure relief valve 24, the electrical signal means 44, and the pressure sensitive means 22 is'shown. v i f The pressure relief valve 24 is of identical construction to those described in FIGS. 2 and 4.

The electrical signal means 44 is comprised of the electrical power source 86 connected in series to the electrical signal indicator 88 and the pressure responsive circuit element 90 The electrical power source 86 is any convenient source which can provide the energy necessary to'energize electrical signal means 44, such as a plurality of turns of the secondary winding 18 or a separate winding on the core 14, or a step-down transformer. The electrical signal indicator 88 in this embodiment, is located at a remote position from the transformer itself. As will be discussed herein, this em-. bodiment of the invention can provide an output volt age across the electrical signal indicator 88 that is proportional to the pressure within the casing 12. An auxiliary circuit means illustrated in FIG. 8 can be utilized in conjunction with the electrical signal indicator 88 I and provide information to the observers in the remote location relative to the transformers operating characteristics. The pressure responsive circuit element 90 of the electrical signal means 44 is a variable resistor 150. The circuit configuration in this embodiment is continuously closed.

In this embodiment of the invention, the pressure sensitive means is comprised of a pressure transducer 152. The transducer 152 is comprised of a pressure sensitive element 154 which is connected to and controls the movement of a movable arm 156. In the embodiment of FIG. 7, the pressure sensitive element 154 is comprised of a piston 158 movable-within a cylinder and biased by a-spring 162. The pressure sensitive element 154 responds to pressure changes with the easing 12 by movement of the piston 158 within the cylinder 160 against the spring bias 162. The movable arm 156 is attached to the piston 158 and moves with the 1 When the pressure within casing 12 exceeds the predetermined value, the pressure relief valve 24 becomes operable. lt is also desirable thatsome signal that the pressure has exceeded the critical value be brought to the attention of the observers. in the remote location. FIG. 8 shows a typical circuit arrangement which can be utilized to carry out this function. In the configuration illustrated in FIG. 8, a spring-loaded, normally closed push buttom 164 is connected in series with a voltage sensing means 166 and a relay coil 168. Relay contacts 170 shunt the voltage sensing means 166 and an auxiliary signal indicator 172 shunts the relay coil 168. This circuit is energized by electrical power means 174. The voltage sensing means 166 is connected to the output terminals 89 of the electrical signal means 44. When the pressure within the casing 12 reaches the value sufficient to operate the pressure relief valve 24, a voltage proportional to this pressure will be sensed by the voltage sensing means 166. If this critical voltage value is detected by the voltage sensing means 166, the auxiliary signal indicator circuit will be completed. When this circuit in the remote observer location is completed, the relay coil 168 is energized and the relay contacts 170 are closed, locking in the relay coil 168. The auxiliary signal indicator 172, usually an indicator light, is also energized. As the pressure relief valve 24 operates. and the critical pressure within the transformer casing 12 is relieved, the auxiliary signal indicator 172 will remain activated. The completed auxiliary signal indicator 172 circuit will remain energized until the push button 164 is manually reset. When the push button 164 is manually reset, the relay coil 168 will be de-energized, the relay contacts 170, in series with the relay coil 168, will be opened, and the auxiliary signal indicator 172 will be deactivated.

Utilization of this invention will provide a method for providing a continuous indication to a remote observer of the pressure level with the transformer 10, as well as providing means for indicating the pressure accumulation within the casing 12 which has exceeded the predetermined value.

Referring now to FIG. 9, a diagrammatic view of an alternate transducer for use in the embodiment of FIG. 7 is shown. The transducer unit 152 is comprised of a transducer housing 176 having a plurality of resilient convolutions 178 thereon. The housing 176 has a face plate 180 at one end thereof. The housing 176 is provided with a plurality of screw threads 182 to permit ease of insertion into the interior of the casing 12. The housing 176 is inserted into the casing 12 so that the face plate 180 is exposed to the pressures within the casing 12. Attached to the underside of the face plate 180 so as to be disposed within the housing 27 is a magnet plunger 184. The plunger 184 is attached to the face plate 180 by a suitable attachment, illustrated in the drawings by a weld 186. A coil 188 is disposed within the housing 176 so as to axially surround theplunger 184. The coil 188 remains fixed relative to the plunger 184. Coil 188 is connected to an amplifier 190, and the amplifier leads exit the housing 176 through a set of openings 192 in the housing 176. The terminals 88 are connected to the electrical sensing means 166 and provide a record of the pressure variations with the casing 12.

As the pressure within the casing 12 increases, the

' face plate 180 compresses the resilient convolutions 178. if the pressure within the casing 12 decreases, the

resilient convolutions 178 expand. The movement of the face plate 180 causes the magnetic plunger 184 to move in or out of the fixed coil 188. Movement of the magnetic plunger 184 relative to the fixed coil 188 induces a voltage in the coil 188. The voltage is amplified by the amplifier 190 and transmitted to an external observer. The voltage fluctuations detectable across the terminals 89 then indicate the pressure variations within the casing 12.

From the foregoing description and the drawings, it is seen that this invention provides an improved arrangement for detecting the existence of excess pressure in a transformer casing, and improved means for relieving any existing excess pressure, beyond a predetermined value, before the transformer casing is damaged.

I claim:

1. A transformer comprising:

a casing,

a magnetic core having windings thereon positioned within said casing,

a dielectric fluid surrounding said core and windings,

pressure relief means for relieving excess pressure developed within said casing, said pressure relief means being displaceable from a first position to a second position when said pressure within said casing reaches a first predetermined value, said pressure relief means in said second position relieving said excess pressure within said casing, and

electric signal means'cooperatively associated with said pressure relief means, said electric signal means being operable when said pressure within said casing reaches said first predetermined value, said electric signal means indicatingthe displacement of said pressure relief means when said pressure within said casing reaches said first predetermined value,

said pressure relief means returning to said first position after relieving said excess pressure within said casing,

said electric signal means continuing to indicate that said excess pressure within said casing has been relieved by said pressure relief means after said pressure relief means returns to said first position.

2. The transformer of claim 1 wherein said pressure relief means comprises a cylinder mounted external to said casing, said cylinder having a pressure relief vent therein, a piston movably disposed within said cylinder, bias means for biasing said piston toward a first position within said cylinder, said'first position being a first predetermined distance in said cylinder from said pressure relief vent, said piston being displaced from said first position within said cylinder for a distance greater than said first predetermined distance when said pressure within said casing reaches said first predetermined value, the displacement of said piston in said cylinder for said distance greater than said first predetermined distance relieving said excess pressure within said casing.

3. The transformer of claim 2, wherein said electric signal means cooperatively associated with said pressure relief means comprises, in series, an electric power source, signal indicator means connected to said electric power source, and a pressure responsive circuit ele ment connected to said signal indicator means, said 1 1 pressure responsive circuit element being operable when said pressure within said casing reaches said first predetermined value, said pressure responsive circuit element responding to said first predetermined value of pressure withinsaid casing by causing said signal indicator means to indicate that said pressure relief means has operated to relieve said excess pressure within said casing.

4. A transformer comprising:

a casing; a magnetic core having windings thereon positioned within said casing; a dielectric fluid surrounding said core and said windings; I pressure relief means for relieving excess pressure developed within said casing, said pressure relief means comprising; I

a cylinder mounted external to said casing, said cylinder having a pressure relief vent therein,

a piston movably disposed within said cylinder, a spring biasing said piston toward a first position within said cylinder, saidfirst position being a first predetermined distance in said cylinder from said pressure relief vent,

said piston being displaced from said first position within said cylinder for a distance greater than said first predetermined distance when said pressure within said'casing reaches a first predetermined value, said displacementof said piston in said cylinder for said distance greater than said firstpredetermined distance relieving said excess pressure from within said casing; and electric signal means cooperatively associated with said pressure relief means, said electric signal means comprising, in series,

an electric power source,

signal indicator means connected to said electric power source,and,

a pressure responsive circuit element connected to said signal indicator means,-said pressure responsive circuit element being operable when said pressure within said casing reaches said first predetermined value; said pressure responsive circuit element responding to said first predetermined value of pressure within said casing by causing said signal indicator means to indicate that said pressure relief means has operated to relieve said excess pressure within said casing; said piston being returned to'said first position within said cylinder by said spring when said excess pres sure within saidca'sing has been relieved;

said signal indicator means continuing to indicate that said excess pressure within said casing has been relieved by operation of said pressure relief means after said piston returns to said first position within said cylinder.

5. The transformer of claim 4, wherein said pressure responsive circuit element comprises:

a horizontal stem connected to said piston,

a vertical stem supported within said casing and biased toward afirst position within said casing, said vertical stem abutting against said horizontal stem until said piston is displaced within said cylinder for said distance greater than said first predetermined distance,

stem, said conducting pin member being electrically connected to said electric power source,

a non-conducting guide member having a slot therein, said conducting pin being slidably disposed within said guide member,

a conducting seat member disposed withinsaid guide member, said conducting seat being electrically connected to said signal indicator means, said conducting pin and said conducting seat being separated when said abutmentbetween said vertical stem and said horizontal stem is intact,

said displacement of said piston within said cylinder for said distance greater than said first predetermined distance breaking said abutment between said vertical stem and said horizontal stem to permit said conducting pin to slide within said guide member to contact said conducting seat,

contact between said conducting pin and said conducting seat activating said signal indicator means to indicate operationof said pressure relief means,

said signal indicator means remaining activated after said piston is returned to said first position within said cylinder after said excess pressure within said casing has been relieved by said pressure relief means.

6. The transformer of claim 4, wherein said pressure responsive circuit element comprises,

a pilot cylinder disposed external to said casing, a pilot piston movably disposed within said pilot cylinder, said pilot piston being exposed to said pressure within said casing, I

a pilot spring biasing said pilot piston toward a first and supporting said second conducting memberwhile said pilot piston is in said first position within said pilot cylinder, contact between said first conducting member and said second'conducting member activating said signal indicator means,

said pilot piston being displaced from said first position within said pilot cylinder when said pressure within said casing reaches said first predetermined value, M V

displacement of said pilot piston within said pilot cylinder breaking said contact between said first conducting member and said second conducting member to de-activate said signal indicator means,

said pilot piston being returned to said first position within said pilot cylinder by said pilot spring when 'said excess pressure within casing is relieved by said pressure relief means, said signal indicator means remaining de-activated to indicate operation of said pressure relief means to relieve said excess pressure within said casing.

7. The transformer of claim 4, wherein said pressure responsive circuit element comprises,

a pilot cylinder disposed external to said casing,

a pilot piston movably disposed within said pilot cylinder, said pilot piston being exposed to said pressure within said casing,

a pilot spring biasing said pilot piston toward a first position within said pilot cylinder,

a bracket attached to said pilot cylinder external to said casing,

a conducting member pivotally mounted external to said casing, said conducting member being electrically connected to said electric power source,

a conducting seat disposed within said casing, said conducting seat being electrically connected to said signal indicator means,

said bracket abutting against and supporting said conducting member while said pilot piston is in said first position within said pilot cylinder, said conducting member and said conducting seat being separated when said abutment between said conducting member and said bracket is intact,

said pilot piston being displaced from said first position within said pilot cylinder when said pressure within said casing reaches said first predetermined value,

displacement of said pilot piston within said pilot cylinder breaking said abutment between said conducting member and said bracket, breaking of said abutment permitting said conducting bar to pivot toward and contact said conducting seat,

contact between said conducting member and said conducting seat activating said signal indicator means to indicate operation of said pressure relief means,

said pilot piston being returned to said first position within said pilot cylinder by said pilot spring when said excess pressure within said casing is relieved by said pressure relief means, said signal indicator means remaining activated to indicate operation of said pressure relief means to relieve said excess pressure within said casing.

8. The transformer of claim 4, wherein said pressure responsive circuit element comprises,

a pilot cylinder disposed within said casing,

a pilot piston disposed within said pilot cylinder,

a pilot spring biasing said pilot piston to a first position within said pilot cylinder,

a variable resistor having said electric power source continuously connected thereto,

means for changing the resistance of said variable resistor, said resistance changing means being attached to saidpilot piston, said changing means being connected electrically to an electric signal relay, said electric signal relay being connected to said signal indicator means,

said pilot piston being displaced from said first position within said pilot cylinder when said pressure within said casing reaches said first predetermined value, displacement of said pilot piston in said pilot cylinder changing the resistance of said variable resistor to a predetermined value, said pedetermined value of resistance of said variable resistor causing a predetermined voltage to be impressed upon said electric signal relay, said predetermined voltage energizing said electric signal relay to activate said signal indicator means,

activation of said signal indicator means indicating operation of said pressure relief means,

said pilot piston being returned to said first position within said pilot cylinder by said pilot spring when said excess pressure within said casing is relieved by said pressure relief means, said signal indicator means remaining activated to indicate operation of said pressure relief means to relieve said excess pressure within said casing.

9. The transformer of claim 4, wherein said pressure responsive circuit element comprises,

a resilient bellows device disposed within said casing, said bellows having a magnet member therein, a coil surrounding said magnet member, said coil being maintained stationary with respect to said magnet member, said coil being connected to an electric signal relay,

said resilient bellows being compressed a predetermined amount when said pressure within said casing reaches said first predetermined value,

compression of said resilient bellows displacing said magnet member within said coil to induce a predetermined voltage within said coil,

said predetermined voltage induced within said coil being impressed upon said electric signal relay, said electric signal relay being energized by said predetennined voltage to activate said signal indicator means,

activation of said signal indicator means indicating operation of said pressure relief means,

said resilient bellows expanding when said excess pressure within said casing is relieved by said pressure relief means, said signal indicator means remaining activated to indicate operation of said pressure relief means to relieve said excess pressure'within said casing. 

1. A transformer comprising: a casing, a magnetic core having windings thereon positioned within said casing, a dielectric fluid surrounding said core and windings, pressure relief means for relieving excess pressure developed within said casing, said pressure relief means being displaceable from a first position to a second position when said pressure within said casing reaches a first predetermined value, said pressure relief means in said second position relieving said excess pressure within said casing, and electric signal means cooperatively associated with said pressure relief means, said electric signal means being operable when said pressure within said casing reaches said first predetermined value, said electric signal means indicating the displacement of said pressure relief means when said pressure within said casing reaches said first predetermined value, said pressure relief means returning to said first position after relieving said excess pressure within said casing, said electric signal means continuing to indicate that said excess pressure within said casing has been relieved by said pressure relief means after said pressure relief means returns to said first position.
 2. The transformer of claim 1 wherein said pressure relief means comprises a cylinder mounted external to said casing, said cylinder having a pressure relief vent therein, a piston movably disposed within said cylinder, bias means for biasing said piston toward a first position within said cylinder, said first position being a first predetermined distance in said cylinder from said pressure relief vent, said piston being displaced from said first position within said cylinder for a distance greater than said first predetermined distance when said pressure within said casing reaches said first predetermined value, the displacement of said piston in said cylinder for said distance greater than said first predetermined distance relieving said excess pressure within said casing.
 3. The transformer of claim 2, wherein said electric signal means cooperatively associated with said pressure relief means comprises, in series, an electric power source, signal indicator means connected to said electric power source, and a pressure responsive circuit element connected to said signal indicator means, said pressure responsive circuit element being operable when said pressure within said casing reaches said first predetermined value, said pressure responsive cIrcuit element responding to said first predetermined value of pressure within said casing by causing said signal indicator means to indicate that said pressure relief means has operated to relieve said excess pressure within said casing.
 4. A transformer comprising: a casing; a magnetic core having windings thereon positioned within said casing; a dielectric fluid surrounding said core and said windings; pressure relief means for relieving excess pressure developed within said casing, said pressure relief means comprising; a cylinder mounted external to said casing, said cylinder having a pressure relief vent therein, a piston movably disposed within said cylinder, a spring biasing said piston toward a first position within said cylinder, said first position being a first predetermined distance in said cylinder from said pressure relief vent, said piston being displaced from said first position within said cylinder for a distance greater than said first predetermined distance when said pressure within said casing reaches a first predetermined value, said displacement of said piston in said cylinder for said distance greater than said first predetermined distance relieving said excess pressure from within said casing; and electric signal means cooperatively associated with said pressure relief means, said electric signal means comprising, in series, an electric power source, signal indicator means connected to said electric power source, and, a pressure responsive circuit element connected to said signal indicator means, said pressure responsive circuit element being operable when said pressure within said casing reaches said first predetermined value, said pressure responsive circuit element responding to said first predetermined value of pressure within said casing by causing said signal indicator means to indicate that said pressure relief means has operated to relieve said excess pressure within said casing; said piston being returned to said first position within said cylinder by said spring when said excess pressure within said casing has been relieved; said signal indicator means continuing to indicate that said excess pressure within said casing has been relieved by operation of said pressure relief means after said piston returns to said first position within said cylinder.
 5. The transformer of claim 4, wherein said pressure responsive circuit element comprises: a horizontal stem connected to said piston, a vertical stem supported within said casing and biased toward a first position within said casing, said vertical stem abutting against said horizontal stem until said piston is displaced within said cylinder for said distance greater than said first predetermined distance, a conducting pin member disposed on said vertical stem, said conducting pin member being electrically connected to said electric power source, a non-conducting guide member having a slot therein, said conducting pin being slidably disposed within said guide member, a conducting seat member disposed within said guide member, said conducting seat being electrically connected to said signal indicator means, said conducting pin and said conducting seat being separated when said abutment between said vertical stem and said horizontal stem is intact, said displacement of said piston within said cylinder for said distance greater than said first predetermined distance breaking said abutment between said vertical stem and said horizontal stem to permit said conducting pin to slide within said guide member to contact said conducting seat, contact between said conducting pin and said conducting seat activating said signal indicator means to indicate operation of said pressure relief means, said signal indicator means remaining activated after said piston is returned to said first position within said cylinder after said excess pressure within said casing has been relieved by said pressure relief means.
 6. The transformer of claim 4, wherein said pressure responsive circuit element comprises, a pilot cylinder disposed external to said casing, a pilot piston movably disposed within said pilot cylinder, said pilot piston being exposed to said pressure within said casing, a pilot spring biasing said pilot piston toward a first position within said pilot cylinder, a bracket member attached to said pilot cylinder external to said casing, a first conducting member connected to said bracket, said first conducting member being electrically connected to said signal indicator means; a second conducting member mounted external to said casing, said second conducting member being electrically connected to said electric power source, said first conducting member contacting and supporting said second conducting member while said pilot piston is in said first position within said pilot cylinder, contact between said first conducting member and said second conducting member activating said signal indicator means, said pilot piston being displaced from said first position within said pilot cylinder when said pressure within said casing reaches said first predetermined value, displacement of said pilot piston within said pilot cylinder breaking said contact between said first conducting member and said second conducting member to de-activate said signal indicator means, said pilot piston being returned to said first position within said pilot cylinder by said pilot spring when said excess pressure within casing is relieved by said pressure relief means, said signal indicator means remaining de-activated to indicate operation of said pressure relief means to relieve said excess pressure within said casing.
 7. The transformer of claim 4, wherein said pressure responsive circuit element comprises, a pilot cylinder disposed external to said casing, a pilot piston movably disposed within said pilot cylinder, said pilot piston being exposed to said pressure within said casing, a pilot spring biasing said pilot piston toward a first position within said pilot cylinder, a bracket attached to said pilot cylinder external to said casing, a conducting member pivotally mounted external to said casing, said conducting member being electrically connected to said electric power source, a conducting seat disposed within said casing, said conducting seat being electrically connected to said signal indicator means, said bracket abutting against and supporting said conducting member while said pilot piston is in said first position within said pilot cylinder, said conducting member and said conducting seat being separated when said abutment between said conducting member and said bracket is intact, said pilot piston being displaced from said first position within said pilot cylinder when said pressure within said casing reaches said first predetermined value, displacement of said pilot piston within said pilot cylinder breaking said abutment between said conducting member and said bracket, breaking of said abutment permitting said conducting bar to pivot toward and contact said conducting seat, contact between said conducting member and said conducting seat activating said signal indicator means to indicate operation of said pressure relief means, said pilot piston being returned to said first position within said pilot cylinder by said pilot spring when said excess pressure within said casing is relieved by said pressure relief means, said signal indicator means remaining activated to indicate operation of said pressure relief means to relieve said excess pressure within said casing.
 8. The transformer of claim 4, wherein said pressure responsive circuit element comprises, a pilot cylinder disposed within said casing, a pilot piston disposed within said pilot cylinder, a pilot spring biasing said pilot piston to a first position within said pilot cylinder, a variable resistor having said electric power source continuously connected thereto, means for changing the resistance of said variable resistor, said resistance changing means being attached to said pilot piston, said changing means being connected electrically to an electric signal relay, said electric signal relay being connected to said signal indicator means, said pilot piston being displaced from said first position within said pilot cylinder when said pressure within said casing reaches said first predetermined value, displacement of said pilot piston in said pilot cylinder changing the resistance of said variable resistor to a predetermined value, said pedetermined value of resistance of said variable resistor causing a predetermined voltage to be impressed upon said electric signal relay, said predetermined voltage energizing said electric signal relay to activate said signal indicator means, activation of said signal indicator means indicating operation of said pressure relief means, said pilot piston being returned to said first position within said pilot cylinder by said pilot spring when said excess pressure within said casing is relieved by said pressure relief means, said signal indicator means remaining activated to indicate operation of said pressure relief means to relieve said excess pressure within said casing.
 9. The transformer of claim 4, wherein said pressure responsive circuit element comprises, a resilient bellows device disposed within said casing, said bellows having a magnet member therein, a coil surrounding said magnet member, said coil being maintained stationary with respect to said magnet member, said coil being connected to an electric signal relay, said resilient bellows being compressed a predetermined amount when said pressure within said casing reaches said first predetermined value, compression of said resilient bellows displacing said magnet member within said coil to induce a predetermined voltage within said coil, said predetermined voltage induced within said coil being impressed upon said electric signal relay, said electric signal relay being energized by said predetermined voltage to activate said signal indicator means, activation of said signal indicator means indicating operation of said pressure relief means, said resilient bellows expanding when said excess pressure within said casing is relieved by said pressure relief means, said signal indicator means remaining activated to indicate operation of said pressure relief means to relieve said excess pressure within said casing. 